The Towa Seiden HL-400 Paddle Type Level Switch is a globally recognized, high-precision point level detection instrument manufactured by Towa Seiden Industrial Co., Ltd. (Japan). Engineered with an ultra-compact footprint, the HL-400 model is widely regarded as the premier worldwide standard for level monitoring within plastic injection molding hoppers, resin drying hoppers, and small ingredient silos where interior mounting space is tightly restricted.

The operational mechanism of the Towa Seiden HL-400 utilizes an electromechanical torque-reaction principle with integrated motor overload protection:
- Under unconstrained conditions (when bulk material has not reached the sensing paddle): A low-speed internal synchronous motor drives the paddle continuously at approximately 1 revolution per minute (RPM).
- When bulk material rises and restricts paddle rotation: The mechanical resistance exerted by the surrounding pellets or powder stops the paddle. The resulting reactive torque causes the suspended motor assembly to rotate around its internal axis, tripping an integrated microswitch. This instantly changes the electrical state of the SPDT output contact to trigger alarms, halt feeding conveyors, or shut down supply valves. Concurrently, a secondary internal contact automatically de-energizes the drive motor. By removing electrical power while the paddle remains stalled in material, motor coil burnout is entirely prevented, ensuring outstanding longevity.
- When the material level falls (releasing the paddle): A precision return spring pulls the motor assembly back to its starting position, resetting the SPDT microswitch contacts and restoring electrical power to resume paddle rotation.

The wetted measuring paddle and drive shaft are fabricated from high-grade SUS304 (AISI 304) stainless steel, offering high resistance to mechanical abrasion while ensuring zero contamination of sensitive process media. The upper housing is precision-cast from heavy-duty industrial aluminum alloy (ADC12) finished with electrostatic powder coating, providing IP65 dust and water ingress protection. Featuring an industry-standard R 3/4" (PT 3/4" / G 3/4") process mounting thread, the Towa Seiden HL-400 enables quick horizontal side-wall or vertical top-cover installation, providing dependable, maintenance-free performance across automated material handling lines.

• Manufacturer: Towa Seiden Industrial Co., Ltd.
• Country of Origin: Japan
• Complete Part Number: Towa Seiden HL-400
• Product Category: Compact Paddle Type Level Switch (Rotary level sensor)
• Operating Principle: Electromechanical torque-reaction with automatic motor cut-off
• Supply Voltage Ratings: 100V AC, 110V AC, 200V AC, 220V AC (50/60 Hz) or optional 24V DC
• Power Consumption: Approximately 1.5 W to 2.5 W
• Paddle Rotational Speed: Approximately 1 RPM (at 50 Hz) / 1.2 RPM (at 60 Hz)
• Electrical Output Contact: 1 SPDT microswitch (Single-Pole Double-Throw)
• Contact Rating: 250V AC, 3A / 5A (Resistive load)
• Detectable Apparent Density: Approx. 0.2 g/cm³ or greater (Suitable for plastic pellets, grains, and industrial powders)
• Mechanical Process Mounting: Male thread R 3/4" (Optional G 3/4", NPT 3/4", or mounting flanges upon request)
• Standard Immersion Length (L): 85 mm (Measured from thread hex shoulder to paddle tip) or custom extended
• Paddle Geometry: Standard single-vane or folding paddle in SUS304 stainless steel
• Wetted Materials:
  - Shaft and Paddle: Stainless Steel SUS304 (AISI 304)
  - Shaft Seal: Abrasion-resistant Nitrile rubber (NBR) or high-temperature packing seal
• Housing Enclosure Material: Heavy-duty aluminum diecast (ADC12)
• Maximum Process Operating Pressure: Up to 196 kPa (approx. 2.0 bar / atmospheric pressure)
• Process Operating Temperature Range: -10°C to +70°C (High-temp versions extendable up to 120°C)
• Ambient Operating Temperature Range: -10°C to +50°C
• Ingress Protection Rating: IP65 (per IEC/EN 60529 standard)
• Net Product Weight: Approximately 1.2 kg